The invention relates to a crankshaft drive for an internal-combustion engine and a method of making a crankshaft for an internal combustion engine, in particular for a motorcycle.
It is known from the prior art to balance an internal-combustion engine having a V-shaped arrangement of cylinders with a balancing shaft provided with a balancing weight for the balancing of first-order masses. In particular, U.S. Pat. No. 5,850,764 issued to Bosetelmann et al discloses mounting a balancing weight parallel to the crankshaft. However, because of the distance between the balancing shaft and the crankshaft, an undesirable additional residual moment is produced which causes corresponding oscillation excitation of the engine, in particular at higher speeds. To eliminate this residual moment, U.S. Pat. No. 5,850,764 proposes an additional shaft which is arranged in the cylinder head and exerts about the crankshaft a moment of equally great magnitude, but acting in the opposite direction to the residual moment of the balancing shaft. However, the additional structural measures necessitated by the inclusion of the balancing shaft take up additional space within the engine. Also, the balancing shaft is subjected to mass forces and may bend or deform the balancing shaft.
The present invention provides an improved motorcycle engine having a crankshaft, a balancing shaft substantially parallel to the crankshaft, a balancing weight coupled to the balancing shaft, and a recess in the balancing weight which allows the connecting rod to clear the balancing weight as the crankshaft and the connecting rod rotate. The inclusion of the recess in the balance weight makes it possible to reduce the distance between the balancing shaft and the crankshaft without allowing the connecting rod to contact the balancing weight during operation of the engine. This in turn reduces the residual moment caused by the balancing shaft and the balancing weight. As a result of this measure, additional, structurally complex measures for reducing the residual moment can advantageously be dispensed with. Additionally, there is a corresponding reduction in the space required for the crankshaft and the balancing shaft.
In one aspect of the present invention, an inexpensive balancing shaft is formed by machining a balancing shaft from a single piece of material. Preferably, an output gear is press fit onto one end of the balancing shaft. The opposite end of the balancing shaft is machined to form a bearing journal. A balancing weight can then be welded onto one side of the balancing shaft. Finally, a recess is machined into one side of the balancing shaft. This recess allows the connecting rods to rotate along their path, constrained by the crankshaft, without contacting the balancing weight or the balancing shaft.
The balancing shaft is preferably rotated by the output gear. The output gear is itself driven by the drive gear, which is preferably coupled directly to the crankshaft. In other embodiments of the present invention, the balancing shaft can be driven in other ways using other elements and configurations of those elements, including intermediate gears, chains, belts, and the like. These other configurations are well known in the art of internal-combustion engine design and are not described in greater detail herein.
In another aspect of the present invention, the recess extends from the balancing weight into the balancing shaft. In this aspect, there is a relatively large recess in the balancing shaft, thereby allowing a greater reduction in the distance between the balancing shaft and the crankshaft.
A rib is preferably formed on one side of the balancing shaft to provide the balancing shaft with additional resistance to bending and deformation. Most preferably, the rib is located between the bearing journals, thereby strengthening the balancing shaft at the weakest point. The rib preferably has a recess through which the connecting rod can pass without contacting the rib. Further advantageous embodiments and improvements of the crankshaft drive and methods of using the crankshaft drive according to the invention for an internal-combustion engine are described below.